Method for evaluating crack resistance of cement-based material for reinforcing concrete column

Abstract

The invention provides a crack resistance evaluation method of a cement-based material for reinforcing a concrete column, and relates to the technical field of concrete. The method for evaluating the crack resistance of the cement-based material for reinforcing the concrete column comprises the following steps: determining material parameters and size parameters of a ring constraint test device; a ring constraint test is carried out, and ring strain development of the inner surface of the steel ring is monitored until the concrete ring cracks or the test is carried out to the 28d age; and determining the crack resistance of the reinforced cement-based material. According to the method for evaluating the crack resistance of the cement-based material for reinforcing the concrete column based on the ring constraint test, provided by the invention, a quantitative calculation method for the constraint degree and an equivalent method for evaluating the stress state of the reinforced concrete under the constraint of the steel ring and the constraint of the existing concrete column are provided; the problem that the constraint degree of the crack resistance test of the existing cement-based material for reinforcing the concrete column is not matched with the actual constraint degree is solved, and the method is easy to operate, accurate and effective.

Description

Technical Field

[0001] The present disclosure relates to the field of concrete technology, and more particularly to a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring restraint test. Background Art

[0002] Concrete early cracking tests mainly include flat plate restrained shrinkage cracking test, prism restrained shrinkage cracking test and ring restrained shrinkage cracking test.

[0003] In the flat plate restrained shrinkage cracking test and the prismatic restrained shrinkage cracking test, the stress state of the restrained concrete is far different from the actual stress state of the concrete in the column reinforcement. The test results can only qualitatively evaluate the quality of the concrete's crack resistance, and cannot accurately predict the restrained cracking of the reinforced concrete, and thus cannot effectively guide the adjustment of concrete performance.

[0004] The stress state of concrete in the ring-type restrained shrinkage cracking test is consistent with the actual stress state of concrete when reinforcing concrete columns. Compared with other tests, it is the most direct test to reflect the shrinkage cracking performance of concrete under reinforcement constraints.

[0005] The conventional ring restraint test is a common ring-restrained shrinkage cracking test. By testing the cracking time of different concretes under the condition of steel ring restraint, the crack resistance of each other can be qualitatively judged. Since the device size of the conventional ring restraint test is relatively fixed, it cannot reflect the restrained cracking of reinforced concrete of concrete columns with different diameters, which has great limitations. Therefore, it is necessary to propose an equivalent method that can accurately reflect the actual restraint of concrete column reinforcement materials and a more scientific and reasonable method for quantitatively evaluating the cracking performance of concrete column reinforcement materials. Summary of the invention

[0006] In view of this, the present disclosure provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring constraint test, so as to solve the problem that the constraint degree of the anti-cracking performance test of cement-based materials for concrete column reinforcement is inconsistent with the actual constraint degree.

[0007] To achieve the above-mentioned purpose, the present disclosure provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement, comprising: determining material parameters and dimensional parameters of a ring constraint test device; conducting a ring constraint test to monitor the development of annular strain on the inner surface of a steel ring until cracks appear in the concrete ring or the test is terminated at the age of 28 days; and determining the anti-cracking performance of the reinforced cement-based material.

[0008] In the above scheme, the method of determining the material parameters and size parameters of the ring constraint test device includes:

[0009] S1: According to the reinforcement scheme of the existing concrete column, the material parameters of the existing concrete column and the reinforced cement-based material are obtained, including the radius r of the existing concrete column 0 , elastic modulus E 3 , Poisson's ratio μ 3 , thickness of reinforced cement-based material h 0 , elastic modulus E 1 , Poisson's ratio μ 1 、The shrinkage value ε corresponding to the age of 28d 0 (28d) and tensile strength f t ;

[0010] S2: Determine the material parameters of the ring constraint test device, the ring constraint test device includes a steel ring and a concrete ring, the steel ring is made of Q345 or higher steel material, and the concrete ring is made of the reinforced cement-based material described in the reinforcement scheme;

[0011] S3: Determine the size parameters of the ring constraint test device, including the inner and outer surface radius and height of the steel ring and the concrete ring, wherein the inner surface radius r of the steel ring is 1 and the outer surface radius r 2 Through the constraint equivalent analysis, it is determined that the inner surface radius of the concrete ring and the outer surface radius r of the steel ring 2 The same thickness as the thickness of the cement-based material in the reinforcement scheme h 0 The same, that is, the inner surface radius of the concrete ring is r 2 , the outer surface radius is r 2 +h 0 .

[0012] In the above scheme, the inner surface radius r of the steel ring in step S3 is 1 and the outer surface radius r 2 Determined through constraint equivalence analysis, including:

[0013] S301: Initial determination of the inner radius r of the steel ring 1i and the outer surface radius r 2j ;

[0014] S302: Calculation of hoop stress σ of cement reinforcement materials in existing concrete column reinforcement scheme 0,θ (r,28d) and the average hoop stress along the radial direction

[0015] S303: Calculation of hoop stress σ in the concrete ring during the ring restraint test 1,θ (r,28d) and the average hoop stress along the radial direction

[0016] S304: Calculate whether the relative error between the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the ring constraint test is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and the outer surface radius r 2j is the inner surface radius r of the steel ring in the ring constraint test device 1 and the outer surface radius r 2 , it is considered that under this condition, the constraint degree of the concrete ring in the ring constraint test is the same as the constraint degree of the reinforced cement material in the existing concrete column reinforcement scheme, and the constraint degree equivalence analysis is completed; if it is not satisfied, repeat the steps S301-S304 until it is satisfied.

[0017] In the above scheme, the hoop stress σ in step S302 is 0,θ (r,28d) includes the inner surface hoop stress σ 0,θ (r 0 ,28d), hoop stress σ 0,θ (r 0 +h 0 ,28d), internal hoop stress σ 0,θ (r 0 +h 0 / 4,28d),σ 0,θ (r 0 +h 0 / 2,28d)σ 0,θ (r 0 +h 0 ×3 / 4,28d),

[0018] The hoop stress σ of the cement material in the reinforcement scheme for the existing concrete column is calculated in step S302. 0,θ (r,28d), the calculation formula used is:

[0019]

[0020] In formula 1, E 1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and the inner surface hoop stress σ 0,θ (r 0 ,28d) where r is r 0 , hoop stress σ 0,θ (r 0 +h 0 ,28d) where r is r 0 +h 0 , internal hoop stress σ 0,θ (r 0 +h 0 / 4,28d) where r is selected 0+h 0 / 4,σ 0,θ (r 0 +h 0 / 2,28d) where r is r 0 +h 0 / 2,σ 0,θ (r 0 +h 0 ×3 / 4,28d) where r is taken 0 +h 0 ×3 / 4,q 0 The radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the existing concrete column is calculated as follows:

[0021]

[0022] In formula 1-1, E 1 is the elastic modulus of the reinforced cement-based material, μ 1 is the Poisson's ratio of reinforced cement-based materials, E 3 is the elastic modulus of the existing concrete column, μ 3 is the Poisson's ratio of the existing concrete column;

[0023] The calculation of the average radial hoop stress of the cement material in the reinforcement scheme of the existing concrete column in step S302 is as follows:

[0024] The average circumferential stress of the cement material in the reinforcement scheme for the existing concrete column along the radial direction The calculation formula used is:

[0025]

[0026] In the above scheme, the hoop stress σ in step S303 1,θ (r,28d) inner surface hoop stress σ 1,θ (r 2j ,28d), hoop stress σ 1,θ (r 2j +h 0 ,28d), internal hoop stress σ 1,θ (r 2j +h 0 / 4,28d),σ 1,θ (r 2j +h 0 / 2,28d),σ 1,θ (r 2j +h 0 ×3 / 4,28d);

[0027] The calculation of the hoop stress σ of the concrete ring in the ring restraint test in step S303 is 1,θ (r,28d), the calculation formula used is:

[0028]

[0029] In formula 3, E 1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and the inner surface hoop stress σ 1,θ (r 2j ,28d) where r is r 2j , hoop stress σ 1,θ (r 2j +h 0 ,28d) where r is r 2j +h 0 , internal hoop stress σ 1,θ (r 2j +h 0 / 4,28d) where r is selected 2j +h 0 / 4,σ 1,θ (r 2j +h 0 / 2,28d) where r is r 2j +h 0 / 2,σ 1,θ (r 2j +h 0 ×3 / 4,28d) where r is taken 2j +h 0 ×3 / 4,q 1 The radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the steel ring is calculated as follows:

[0030]

[0031] In formula 3-1, E 1 is the elastic modulus of the concrete ring, μ 1 is the Poisson's ratio of the concrete ring, E 2 is the elastic modulus of the steel ring, μ 2 is the Poisson's ratio of the steel ring;

[0032] The calculation step S303 is as follows: the average radial hoop stress of the concrete ring in the ring restraint test The calculation formula used is:

[0033]

[0034] In the above scheme, the step S304 of calculating whether the relative errors of the hoop stress of the cement material in the existing concrete column reinforcement scheme and the hoop stress of the concrete ring in the ring constraint test are both less than 5% specifically includes:

[0035]

[0036] In the above scheme, the height of the steel ring and the concrete ring in step S3 ranges from 8 to 10 cm, and the inner radius r of the steel ring is 1 The value range is (150, 215) mm, the outer radius r 2 The value range is (175, 225) mm.

[0037] In the above scheme, the ring restraint test is carried out to monitor the development of the ring strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is terminated at the age of 28 days, including:

[0038] S401: The steel ring is placed on a flat steel plate at a radius of r 2 Within the range, the steel plate is milled to a depth of 2 to 3 mm to form a concave circular groove to effectively limit the overall horizontal displacement of the steel ring without affecting the compression deformation of the steel ring; the outer radius r of the steel plate 3 Same as the outer radius of the concrete ring, r 3 =r 2 +h 0 , at the outer radius of the steel plate, set the inner diameter r 3 , removable circular steel formwork, 2-3 mm thick, used as the outer formwork for pouring the concrete ring;

[0039] S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete and the outer surface of the steel ring are in close contact but not bonded; spray lubricating oil on the top surface of the steel plate so that the concrete, the steel ring and the steel plate are in close contact but not bonded;

[0040] S403: The strain gauge is arranged horizontally at the half height of the steel ring and along the quarter-divided points of the inner surface of the steel ring. The direction of strain measurement is the circumferential strain of the inner surface of the steel ring.

[0041] S404: Use the strain collector to collect the annular strain ε on the inner surface of the steel ring s,0 (t) until cracks appear in the concrete ring or the test is terminated at the age of 28 days. The strain acquisition accuracy of the strain collector shall not be less than ±1με and the frequency shall not be less than 1 time / min.

[0042] In the above scheme, the determination of the anti-cracking performance of the reinforced cement-based material includes: judging whether cracks appear in the concrete ring during the test; if cracks appear in the concrete ring during the test, the age corresponding to the cracking is used to characterize that the anti-cracking performance of the reinforced cement-based material with cracks is inferior to that of the reinforced cement-based material without cracks; if no cracks appear in the concrete ring during the test, the inner surface circumferential strain ε of the steel ring within the 28d age period is first determined according to the test. s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2 ,28d), and then use the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2 ,28d) and tensile strength f t The ratio determines the crack resistance of the reinforced cement-based material. The smaller the ratio, the better the crack resistance of the reinforced cement-based material.

[0043] In the above scheme, the hoop strain ε of the inner surface of the steel ring within the 28d age period is tested. s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2j ,28d) is calculated as:

[0044]

[0045] In formula 6, ε e (28d) is the effective shrinkage strain of the concrete ring after considering the creep effect, q' is the radial uniform force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring, and the calculation formula is:

[0046]

[0047] ε e (28d) can be obtained by combining equation 6-1 and equation 6-2

[0048]

[0049] In the formula, E 1 is the elastic modulus of the concrete ring, μ 1 is the Poisson's ratio of the concrete ring, E 2 is the elastic modulus of the steel ring, μ 2 is the Poisson’s ratio of the steel ring.

[0050] It can be seen from the above technical solutions that the method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on the ring constraint test provided by the present disclosure has at least the following beneficial effects:

[0051] 1. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns based on the ring constraint test provided by the present invention provides a quantitative calculation method for the degree of constraint and an equivalent method for evaluating the stress state of reinforced concrete under the constraint of a steel ring and under the constraint of an existing concrete column, thereby solving the problem of the inconsistency between the constraint degree of the anti-cracking performance test of cement-based materials for reinforcing existing concrete columns and the actual constraint degree.

[0052] 2. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on the ring constraint test provided in the present invention provides a stress calculation method for reinforced concrete when reinforcing concrete columns and for concrete rings in the ring constraint test. Taking the stress state of reinforced concrete when reinforcing concrete columns as a reference, different degrees of constraint of the steel ring on the concrete ring are achieved by adjusting the size of the steel ring, ensuring that the key points of the concrete ring section and the average stress of the section in the ring constraint test are consistent with the reference state, thereby achieving the ability to simulate the real constraint state of reinforced concrete when reinforcing concrete columns of different diameters.

[0053] 3. Compared with the traditional plane constraint cracking test, the method for evaluating the crack resistance of cement-based materials for concrete column reinforcement based on the ring constraint test provided by the present invention uses a test device that ensures that the stress state of the reinforced concrete in the test is consistent with that in actual engineering applications, and both are in a ring constraint state. The test results can more truly and accurately reflect the state in actual application.

[0054] 4. The present invention provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring constraint test. The ring constraint test device uses a hollow ring to achieve real-time monitoring of the annular strain on the inner surface of the steel ring. It is not affected by the moisture in the concrete after the early pouring of the concrete. The stress development of the reinforced concrete under real constraints can be monitored throughout the entire process since the concrete pouring is completed.

[0055] 5. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on the ring constraint test provided by the present invention has a simple test device and can be reused, avoiding the large workload and cost caused by making full-scale concrete columns for testing, which is very conducive to laboratory promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0057] Figure 1 The present invention is a flowchart of a method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns based on a ring confinement test according to an embodiment of the present disclosure.

[0058] Figure 2Schematic diagram of a ring restraint test device according to an embodiment of the present disclosure.

[0059] Figure 3 Schematic diagram of the position of strain gauges in a ring constraint test device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0060] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0061] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0062] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0063] In order to solve the problem that the test constraint degree of the crack resistance of cement-based materials used to reinforce existing concrete columns does not match the actual constraint degree, such as Figure 1 As shown, the present disclosure provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring restraint test, the method comprising the following steps:

[0064] Step A: Determine the material parameters and size parameters of the ring constraint test device;

[0065] Step B: Conduct a ring restraint test and monitor the development of the ring strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is terminated at 28 days of age;

[0066] Step C: Determine the crack resistance of the reinforced cementitious material.

[0067] In the embodiment of the present disclosure, the step A of determining the material parameters and size parameters of the ring constraint test device includes:

[0068] S1: According to the reinforcement scheme of the existing concrete column, the material parameters of the existing concrete column and the reinforced cement-based material are obtained, including the radius r of the existing concrete column0 , elastic modulus E 3 , Poisson's ratio μ 3 , thickness of reinforced cement-based material h 0 , elastic modulus E 1 , Poisson's ratio μ 1 、The shrinkage value ε corresponding to the age of 28d 0 (28d) and tensile strength f t ;

[0069] S2: Determine the material parameters of the ring constraint test device, the ring constraint test device includes a steel ring and a concrete ring, the steel ring is made of Q345 or higher steel material, and the concrete ring is made of the reinforced cement-based material described in the reinforcement scheme;

[0070] S3: Determine the size parameters of the ring constraint test device, including the inner and outer surface radius and height of the steel ring and the concrete ring, wherein the inner surface radius r of the steel ring is 1 and the outer surface radius r 2 Through the constraint equivalent analysis, it is determined that the inner surface radius of the concrete ring and the outer surface radius r of the steel ring 2 The same thickness as the thickness of the cement-based material in the reinforcement scheme h 0 The same, that is, the inner surface radius of the concrete ring is r 2 , the outer surface radius is r 2 +h 0 , such as Figure 2 and Figure 3 As shown, Figure 2 is a schematic diagram of a ring constraint test device according to an embodiment of the present disclosure, Figure 3 It is a schematic diagram of the position of strain gauges in the ring constraint test device according to an embodiment of the present disclosure, wherein reference numeral 1 is a steel ring, reference numeral 2 is a concrete ring, and reference numeral 3 is a strain gauge.

[0071] Furthermore, the inner surface radius r of the steel ring in step S3 is 1 and the outer surface radius r 2 Determined through constraint equivalence analysis, including:

[0072] S301: Initial determination of the inner radius r of the steel ring 1i and the outer surface radius r 2j ;

[0073] S302: Calculation of hoop stress σ of cement reinforcement materials in existing concrete column reinforcement scheme 0,θ (r,28d) and the average hoop stress along the radial direction

[0074] Wherein, the hoop stress σ in step S302 0,θ(r,28d) includes the inner surface hoop stress σ 0,θ (r 0 ,28d), hoop stress σ 0,θ (r 0 +h 0 ,28d), internal hoop stress σ 0,θ (r 0 +h 0 / 4,28d),σ 0,θ (r 0 +h 0 / 2,28d)σ 0,θ (r 0 +h 0 ×3 / 4,28d),

[0075] The hoop stress σ of the cement material in the reinforcement scheme for the existing concrete column is calculated in step S302. 0,θ (r,28d), the calculation formula used is:

[0076]

[0077] In formula 1, E 1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and the inner surface hoop stress σ 0,θ (r 0 ,28d) where r is r 0 , hoop stress σ 0,θ (r 0 +h 0 ,28d) where r is r 0 +h 0 , internal hoop stress σ 0,θ (r 0 +h 0 / 4,28d) where r is selected 0 +h 0 / 4,σ 0,θ (r 0 +h 0 / 2,28d) where r is r 0 +h 0 / 2,σ 0,θ (r 0 +h 0 ×3 / 4,28d) where r is taken 0 +h 0 ×3 / 4,q 0 The radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the existing concrete column is calculated as follows:

[0078]

[0079] In formula 1-1, E 1 is the elastic modulus of the reinforced cement-based material, μ 1 is the Poisson's ratio of reinforced cement-based materials, E 3 is the elastic modulus of the existing concrete column, μ 3 is the Poisson's ratio of the existing concrete column;

[0080] The calculation of the average radial hoop stress of the cement material in the reinforcement scheme of the existing concrete column in step S302 is as follows:

[0081] The average circumferential stress of the cement material in the reinforcement scheme for the existing concrete column along the radial direction The calculation formula used is:

[0082]

[0083] S303: Calculation of hoop stress σ in the concrete ring during the ring restraint test 1,θ (r,28d) and the average hoop stress along the radial direction

[0084] Wherein, the hoop stress σ in step S303 1,θ (r,28d) inner surface hoop stress σ 1,θ (r 2j ,28d), hoop stress σ 1,θ (r 2j +h 0 ,28d), internal hoop stress σ 1,θ (r 2j +h 0 / 4,28d),σ 1,θ (r 2j +h 0 / 2,28d),σ 1,θ (r 2j +h 0 ×3 / 4,28d);

[0085] The calculation of the hoop stress σ of the concrete ring in the ring restraint test in step S303 is 1,θ (r,28d), the calculation formula used is:

[0086]

[0087] In formula 3, E 1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and the inner surface hoop stress σ 1,θ (r 2j ,28d) where r is r 2j , hoop stress σ 1,θ (r2j +h 0 ,28d) where r is r 2j +h 0 , internal hoop stress σ 1,θ (r 2j +h 0 / 4,28d) where r is selected 2j +h 0 / 4,σ 1,θ (r 2j +h 0 / 2,28d) where r is r 2j +h 0 / 2,σ 1,θ (r 2j +h 0 ×3 / 4,28d) where r is taken 2j +h 0 ×3 / 4,q 1 The radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the steel ring is calculated as follows:

[0088]

[0089] In formula 3-1, E 1 is the elastic modulus of the concrete ring, μ 1 is the Poisson's ratio of the concrete ring, E 2 is the elastic modulus of the steel ring, μ 2 is the Poisson's ratio of the steel ring;

[0090] The calculation step S303 is as follows: the average radial hoop stress of the concrete ring in the ring restraint test The calculation formula used is:

[0091]

[0092] S304: Calculate whether the relative error between the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the ring constraint test is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and the outer surface radius r 2j is the inner surface radius r of the steel ring in the ring constraint test device 1 and the outer surface radius r 2 , it is considered that under this condition, the constraint degree of the concrete ring in the ring constraint test is the same as the constraint degree of the reinforced cement material in the existing concrete column reinforcement scheme, and the constraint degree equivalence analysis is completed; if it is not satisfied, repeat the steps S301-S304 until it is satisfied.

[0093] The step S304 of calculating whether the relative errors of the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the hoop constraint test are both less than 5% specifically includes:

[0094]

[0095]

[0096] Optionally, the height of the steel ring and the concrete ring in step S3 ranges from 8 to 10 cm, and the inner radius r of the steel ring is 1 The value range is (150, 215) mm, the outer radius r 2 The value range is (175, 225) mm.

[0097] In the embodiment of the present disclosure, the ring constraint test described in step B is carried out to monitor the development of the ring strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is terminated at the age of 28 days, including:

[0098] S401: The steel ring is placed on a flat steel plate at a radius of r 2 Within the range, the steel plate is milled to a depth of 2 to 3 mm to form a concave circular groove to effectively limit the overall horizontal displacement of the steel ring without affecting the compression deformation of the steel ring; the outer radius r of the steel plate 3 Same as the outer radius of the concrete ring, r 3 =r 2 +h 0 , at the outer radius of the steel plate, set the inner diameter r 3 , removable circular steel formwork, 2-3 mm thick, used as the outer formwork for pouring the concrete ring;

[0099] S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete and the outer surface of the steel ring are in close contact but not bonded; spray lubricating oil on the top surface of the steel plate so that the concrete, the steel ring and the steel plate are in close contact but not bonded;

[0100] S403: The strain gauge is arranged horizontally at the half height of the steel ring and along the quarter-divided points of the inner surface of the steel ring. The direction of strain measurement is the circumferential strain of the inner surface of the steel ring.

[0101] S404: Use the strain collector to collect the annular strain ε on the inner surface of the steel ring s,0 (t) until cracks appear in the concrete ring or the test is terminated at the age of 28 days. The strain acquisition accuracy of the strain collector shall not be less than ±1με and the frequency shall not be less than 1 time / min.

[0102] In the embodiment of the present disclosure, the step C of determining the anti-cracking performance of the reinforced cement-based material includes: judging whether cracks appear in the concrete ring during the test; if cracks appear in the concrete ring during the test, the age corresponding to the cracking is used to characterize that the anti-cracking performance of the reinforced cement-based material with cracks is inferior to the anti-cracking performance of the reinforced cement-based material without cracks; if no cracks appear in the concrete ring during the test, the hoop strain ε of the inner surface of the steel ring within the 28d age period is first measured. s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2 ,28d), and then use the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2 ,28d) and tensile strength f t The ratio determines the crack resistance of the reinforced cement-based material. The smaller the ratio, the better the crack resistance of the reinforced cement-based material.

[0103] Among them, the hoop strain ε of the inner surface of the steel ring within the 28d test period s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2j ,28d) is calculated as:

[0104]

[0105] In formula 6, ε e (28d) is the effective shrinkage strain of the concrete ring after considering the creep effect, q' is the radial uniform force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring, and the calculation formula is:

[0106]

[0107] ε e (28d) can be obtained by combining equation 6-1 and equation 6-2

[0108]

[0109] In the formula, E 1 is the elastic modulus of the concrete ring, μ 1 is the Poisson's ratio of the concrete ring, E 2 is the elastic modulus of the steel ring, μ 2 is the Poisson’s ratio of the steel ring.

[0110] Based on the above Figure 1The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns based on the ring constraint test is shown. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns based on the ring constraint test provided by the present disclosure is described in detail below in combination with Examples 1-2.

[0111] Embodiment 1: A method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring restraint test, comprising:

[0112] S1: According to the reinforcement scheme of the existing concrete column, the existing concrete column adopts C50 ordinary concrete, and the reinforced cement-based material adopts ultra-high toughness cement-based material ECC-50. The material parameters of the existing concrete column and the reinforced cement-based material are obtained, as shown in Table 1;

[0113] Table 1 Material parameters of existing concrete columns and reinforced cement-based materials

[0114]

[0115] S2: Determine the material parameters of the ring constraint test device, the ring constraint test device includes a steel ring and a concrete ring, the steel ring is made of Q345 steel, that is, the elastic modulus E of the steel ring 2 is 210GPa, and the Poisson's ratio of the steel ring μ 2 is 0.25; the concrete ring is prepared by the reinforced cement-based material described in the reinforcement scheme, that is, the ultra-high toughness cement-based material ECC-50;

[0116] S3: Determine the size parameters of the ring constraint test device, including the inner and outer surface radius and height of the steel ring 1 and the concrete ring 2, wherein the inner surface radius r of the steel ring 1 is 1 and the outer surface radius r 2 It is determined by constraint equivalent analysis. The specific steps are as follows:

[0117] S301: Initial determination of the inner radius r of the steel ring 1i = 0.35m and outer surface radius r 2j =0.4m;

[0118] S302: Calculate the hoop stress σ of the cement material in the reinforcement scheme for existing concrete columns according to equations 1 and 2 0,θ (r,28d) and the average hoop stress along the radial direction

[0119] S303: Calculate the hoop stress σ of the concrete ring in the ring restraint test according to equations 3 and 4 1,θ (r,28d) and the average hoop stress along the radial direction

[0120] S304: Calculate according to Formula 5 whether the relative errors of the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the hoop restraint test are both less than 5%;

[0121] The specific calculation results of S302-S304 are shown in Table 2.

[0122] Table 2 Calculation results of hoop stress and average hoop stress of reinforced cement material and concrete ring

[0123]

[0124] According to the calculation results, the relative error between the hoop stress of the cement material in the existing concrete column reinforcement scheme and the hoop stress of the concrete ring in the ring constraint test is less than 5%, so the inner surface radius r of the steel ring is selected. 1 = 0.35m and outer surface radius r 2 =0.4m.

[0125] The inner radius of the concrete ring 2 and the outer radius of the steel ring 1 are 2 The same thickness as the thickness of the cement-based material in the reinforcement scheme h 0 The same, that is, the inner surface radius of the concrete ring 2 is r 2 , the outer surface radius is r 2 +h 0 , that is, the dimensional parameters of the ring constraint test device are shown in Table 3.

[0126] Table 3 Dimensional parameters of the ring restraint test device

[0127]

[0128] S4: Conduct a ring restraint test to monitor the hoop strain ε on the inner surface of steel ring 1 s,0 (t) development until the test ends at 28 days, and the hoop strain ε of the inner surface of steel ring 1 at 28 days is tested. s,0 (28d) = 10.5με.

[0129] S5: Evaluate the crack resistance of reinforced cement-based materials. Calculate the actual maximum hoop tensile stress σ' of the concrete ring according to Equation 6. 1,θ (r 2 ,28d)=4.42MPa, the actual hoop tensile stress σ' of concrete ring 2 1,θ (r 2 ,28d) and the ratio of tensile strength is 4.42 / 4.8=0.92.

[0130] Embodiment 2: A method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring restraint test, comprising:

[0131] S1: According to the reinforcement scheme of the existing concrete column, the existing concrete column adopts C50 ordinary concrete, and the reinforced cement-based material adopts C80 concrete. The material parameters of the existing concrete column and the reinforced cement-based material are obtained, as shown in Table 4;

[0132] Table 4 Material parameters of existing concrete columns and reinforced cement-based materials

[0133]

[0134] S2: Determine the material parameters of the ring constraint test device, the ring constraint test device includes a steel ring and a concrete ring, the steel ring is made of Q345 steel, that is, the elastic modulus E of the steel ring 2 is 210GPa, and the Poisson's ratio of the steel ring μ 2 is 0.25; the concrete ring is prepared by the reinforced cement-based material described in the reinforcement scheme, that is, C80 concrete;

[0135] S3: Determine the size parameters of the ring constraint test device, including the inner and outer surface radius and height of the steel ring 1 and the concrete ring 2, wherein the inner surface radius r of the steel ring 1 is 1 and the outer surface radius r 2 It is determined by constraint equivalent analysis. The specific steps are as follows:

[0136] S301: Initial determination of the inner radius r of the steel ring 1i = 0.35m and outer surface radius r 2j =0.4m;

[0137] S302: Calculate the hoop stress σ of the cement material in the reinforcement scheme for existing concrete columns according to equations 1 and 2 0,θ (r,28d) and the average hoop stress along the radial direction

[0138] S303: Calculate the hoop stress σ of the concrete ring in the ring restraint test according to equations 3- and 4 1,θ (r,28d) and the average hoop stress along the radial direction

[0139] S304: Calculate according to Formula 5 whether the relative errors of the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the hoop restraint test are both less than 5%;

[0140] The specific calculation results of S302-S304 are shown in Table 5.

[0141] Table 5 Calculation results of hoop stress and average hoop stress of reinforced cement material and concrete ring

[0142]

[0143] According to the calculation results, the relative error between the hoop stress of the cement material in the existing concrete column reinforcement scheme and the hoop stress of the concrete ring in the ring constraint test is less than 5%, so the inner surface radius r of the steel ring is selected. 1 = 0.35m and outer surface radius r 2 =0.4m.

[0144] The inner radius of the concrete ring 2 and the outer radius of the steel ring 1 are 2 The same thickness as the thickness of the cement-based material in the reinforcement scheme h 0 The same, that is, the inner surface radius of the concrete ring 2 is r 2 , the outer surface radius is r 2 +h 0 , that is, the dimensional parameters of the ring constraint test device are shown in Table 6.

[0145] Table 6 Dimensional parameters of the ring restraint test device

[0146]

[0147] S4: Conduct a ring restraint test to monitor the hoop strain ε on the inner surface of steel ring 1 s,0 (t) development until the test ends at 28 days, and the hoop strain ε of the inner surface of steel ring 1 at 28 days is tested. s,0 (28d) = 15.5με.

[0148] S5: Evaluate the crack resistance of reinforced cement-based materials. Calculate the actual maximum hoop tensile stress σ' of the concrete ring according to Equation 6 1,θ (r 2 ,28d)=6.39MPa, the actual hoop tensile stress σ' of concrete ring 2 1,θ (r 2 ,28d) and the ratio of tensile strength is 6.39 / 3.11=2.05.

[0149] Comparison of the actual hoop tensile stress σ' of the concrete ring in Example 1 and Example 2 1,θ (r 2 , 28d) and the ratio of tensile strength, the actual hoop tensile stress σ' of the concrete ring in Example 1 1,θ (r 2 ,28d) and the ratio of tensile strength is less than the actual circumferential tensile stress σ' of the concrete ring in Example 2 1,θ (r 2,28d) to the ratio of tensile strength, the crack resistance of the reinforced cement-based material in Example 1, which is the ultra-high toughness cement-based material ECC, is better than the crack resistance of the reinforced cement-based material in Example 2, which is the ultra-high toughness cement-based material ECC.

[0150] It can be seen from the above embodiments that the present disclosure provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring constraint test, and provides a stress calculation method for reinforced concrete when reinforcing concrete columns and for concrete rings in a ring constraint test. The stress state of reinforced concrete when reinforcing concrete columns is used as a reference, and different degrees of constraint of the steel ring on the concrete ring are achieved by adjusting the size of the steel ring, ensuring that the key points of the concrete ring section and the average stress of the section in the ring constraint test are consistent with the reference state, thereby achieving the ability to simulate the real constraint state of reinforced concrete when reinforcing concrete columns of different diameters.

[0151] Compared with the traditional plane restraint cracking test, the test device adopted in the present invention makes the stress state of the reinforced concrete in the test consistent with that in the actual engineering application, both are in a ring restraint state, and the test results can more truly and accurately reflect the state in actual application.

[0152] The present invention provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring constraint test. The ring constraint test device adopts a hollow ring, which realizes real-time monitoring of the annular strain on the inner surface of the steel ring and is not affected by the influence of moisture in the concrete after the early pouring of the concrete. It can realize the whole process monitoring of the stress development of the reinforced concrete under real constraints since the completion of the concrete pouring.

[0153] The present invention provides a method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement based on a ring restraint test. The test device is simple and can be reused, avoiding the large workload and cost caused by making full-scale concrete columns for testing, which is very conducive to laboratory promotion and application.

[0154] It will be appreciated by those skilled in the art that the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0155] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement, characterized in that: include: Determine the material parameters and size parameters of the ring restraint test device; Conduct ring restraint tests and monitor the development of hoop strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is terminated at 28 days of age; and Determine the crack resistance of reinforced cementitious materials.

2. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement according to claim 1, characterized in that: The method of determining the material parameters and size parameters of the ring constraint test device includes: S1: According to the reinforcement scheme of the existing concrete column, the material parameters of the existing concrete column and the reinforced cement-based material are obtained, including the radius r0, elastic modulus E3, Poisson's ratio μ3 of the existing concrete column, the thickness h0, elastic modulus E1, Poisson's ratio μ1 of the reinforced cement-based material, the shrinkage value ε0 (28d) corresponding to the age of 28d, and the tensile strength f t ; S2: Determine the material parameters of the ring constraint test device, the ring constraint test device includes a steel ring and a concrete ring, the steel ring is made of Q345 or higher steel material, and the concrete ring is made of the reinforced cement-based material described in the reinforcement scheme; S3: Determine the dimensional parameters of the ring constraint test device, including the inner and outer surface radii and heights of the steel ring and the concrete ring, wherein the inner surface radius r1 and the outer surface radius r2 of the steel ring are determined by constraint equivalent analysis, the inner surface radius of the concrete ring is the same as the outer surface radius r2 of the steel ring, and the thickness is the same as the thickness h0 of the reinforced cement-based material described in the reinforcement scheme, that is, the inner surface radius of the concrete ring is r2, and the outer surface radius is r2+h0.

3. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement according to claim 2, characterized in that: In step S3, the inner surface radius r1 and the outer surface radius r2 of the steel ring are determined by constraint equivalent analysis, including: S301: Initial determination of the inner radius r of the steel ring 1i and the outer surface radius r 2j ; S302: Calculation of hoop stress σ of cement reinforcement materials in existing concrete column reinforcement scheme 0,θ (r,28d) and the average hoop stress along the radial direction S303: Calculation of hoop stress σ in the concrete ring during the ring restraint test 1,θ (r,28d) and the average hoop stress along the radial direction S304: Calculate whether the relative error between the hoop stress of the cement material in the reinforcement scheme for the existing concrete column and the hoop stress of the concrete ring in the ring constraint test is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and the outer surface radius r 2j are the inner surface radius r1 and the outer surface radius r2 of the steel ring in the ring constraint test device. It is considered that under this condition, the constraint degree of the concrete ring in the ring constraint test is the same as the constraint degree of the reinforced cement material in the existing concrete column reinforcement scheme, and the constraint degree equivalence analysis is completed; if not satisfied, repeat steps S301-S304 until satisfied.

4. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns according to claim 3, characterized in that: The hoop stress σ in step S302 0,θ (r,28d) includes the inner surface hoop stress σ 0,θ (r0,28d), hoop stress σ 0,θ (r0+h0,28d), internal hoop stress σ 0,θ (r0+h0 / 4,28d),σ 0,θ (r0+h0 / 2,28d)σ 0,θ (r0+h0×3 / 4,28d), The hoop stress σ of the cement material in the reinforcement scheme for the existing concrete column is calculated in step S302. 0,θ (r,28d), the calculation formula used is: In formula 1, E1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and the inner surface hoop stress σ 0,θ (r0,28d) where r is r0 and the hoop stress σ 0,θ (r0+h0,28d) where r is r0+h0, the internal hoop stress σ 0,θ (r0+h0 / 4,28d) where r is r0+h0 / 4, σ 0,θ (r0+h0 / 2,28d) where r is r0+h0 / 2, σ 0,θ (r0+h0×3 / 4,28d) where r is r0+h0×3 / 4, q0 is the radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the existing concrete column. The calculation formula is: In formula 1-1, E1 is the elastic modulus of the reinforced cement-based material, μ1 is the Poisson's ratio of the reinforced cement-based material, E3 is the elastic modulus of the existing concrete column, and μ3 is the Poisson's ratio of the existing concrete column; The calculation of the average radial hoop stress of the cement material in the reinforcement scheme of the existing concrete column in step S302 is as follows: The average circumferential stress of the cement material in the reinforcement scheme for the existing concrete column along the radial direction The calculation formula used is:

5. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement according to claim 4, characterized in that: The hoop stress σ in step S303 1,θ (r,28d) inner surface hoop stress σ 1,θ (r 2j ,28d), hoop stress σ 1,θ (r 2j +h0,28d), internal hoop stress σ 1,θ (r 2j +h0 / 4,28d),σ 1,θ (r 2j +h0 / 2,28d),σ 1,θ (r 2j +h0×3 / 4,28d); The calculation of the hoop stress σ of the concrete ring in the ring restraint test in step S303 is 1,θ (r,28d), the calculation formula used is: In formula 3, E1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and the inner surface hoop stress σ 1,θ (r 2j ,28d) where r is r 2j , hoop stress σ 1,θ (r 2j +h0,28d) in which r is taken as r 2j +h0, internal hoop stress σ 1,θ (r 2j +h0 / 4,28d) where r is r 2j +h0 / 4,σ 1,θ (r 2j +h0 / 2,28d) where r is r 2j +h0 / 2,σ 1,θ (r 2j +h0×3 / 4,28d) where r is r 2j +h0×3 / 4, q1 is the radial uniform force on the inner surface of the reinforced cement material caused by the shrinkage of the reinforced cement material under the constraint of the steel ring, and the calculation formula is: In formula 3-1, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring; The calculation step S303 is as follows: the average radial hoop stress of the concrete ring in the ring restraint test The calculation formula used is:

6. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns according to claim 4, characterized in that: The step S304 of calculating whether the relative errors of the hoop stress of the cement material in the existing concrete column reinforcement scheme and the hoop stress of the concrete ring in the ring restraint test are both less than 5% specifically includes:

7. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns according to claim 2, characterized in that: In step S3, the height of the steel ring and the concrete ring ranges from 8 to 10 cm, the inner radius r1 of the steel ring ranges from (150, 215) mm, and the outer radius r2 ranges from (175, 225) mm.

8. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement according to claim 1, characterized in that: The ring restraint test is carried out to monitor the development of the ring strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is terminated at the age of 28 days, including: S401: The steel ring is placed on a flat steel plate. Within the radius r2 of the steel plate, the steel plate is milled to a depth of 2 to 3 mm to form a concave circular groove, so as to effectively limit the overall horizontal displacement of the steel ring without affecting the compression deformation of the steel ring. The outer radius r3 of the steel plate is the same as the outer radius of the concrete ring, r3 = r2 + h0. At the outer radius of the steel plate, a detachable circular steel template with an inner diameter of r3 and a thickness of 2 to 3 mm is set as the outer template when pouring the concrete ring. S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete and the outer surface of the steel ring are in close contact but not bonded; spray lubricating oil on the top surface of the steel plate so that the concrete, the steel ring and the steel plate are in close contact but not bonded; S403: The strain gauge is arranged horizontally at the half height of the steel ring and along the quarter-divided points of the inner surface of the steel ring. The direction of strain measurement is the circumferential strain of the inner surface of the steel ring. S404: Use the strain collector to collect the annular strain ε on the inner surface of the steel ring s,0 (t) until cracks appear in the concrete ring or the test is terminated at the age of 28 days. The strain acquisition accuracy of the strain collector shall not be less than ±1με and the frequency shall not be less than 1 time / min.

9. The method for evaluating the anti-cracking performance of cement-based materials for concrete column reinforcement according to claim 1, characterized in that: The method of determining the anti-cracking performance of the reinforced cement-based material comprises: Determine whether cracks appear in the concrete ring during the test; If cracks appear in the concrete ring during the test, the age corresponding to the cracking is used as the representation, and the crack resistance of the reinforced cement-based material with cracks is inferior to that of the reinforced cement-based material without cracks; If the concrete ring does not crack during the test, the inner surface hoop strain ε of the steel ring within 28 days of the test is first s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r2,28d), and then use the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r2,28d) and tensile strength f t The ratio determines the crack resistance of the reinforced cement-based material. The smaller the ratio, the better the crack resistance of the reinforced cement-based material.

10. The method for evaluating the anti-cracking performance of cement-based materials for reinforcing concrete columns according to claim 9, characterized in that: According to the test of the hoop strain ε of the inner surface of the steel ring within 28 days s,0 (28d) Calculate the actual maximum hoop tensile stress σ' of the concrete ring 1,θ (r 2j ,28d) is calculated as: In formula 6, ε e (28d) is the effective shrinkage strain of the concrete ring after considering the creep effect, q' is the radial uniform force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring, and the calculation formula is: ε e (28d) can be obtained by combining equation 6-1 and equation 6-2 Where, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

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